United States Patent (19) [11] 3,816,287 Bockmann Et Al

United States Patent (19) [11] 3,816,287 Bockmann et al. (45) June 11, 1974

54) PHOTOLYTIC PROCESS FOR THE 2,695,873 1 / 1954 Loverde...... 204/63 R CONTINUOUS PRODUCTION OF 2,810,688 - 10/1957 Ivins et al...... 204/163 R BENZOTRCHELORIDE WITH A LOW 2,81,486 10/1957 Reynold et al...... 204/163 R BENZAL CHELORIDE CONTENT Primary Examiner-Benjamin R. Padgett 75) Inventors: Walter Bockmann; Rudolf Hornung, Attorney, Agent, or Firm-Burgess, Dinklage & both of Krefeld-Bockum, Germany Sprung 73) Assignee: Bayer Aktiengesellschaft, Leverkusen, Germany 57 ABSTRACT Benzotrichloride is prepared in a continuous process 22 Filed: Oct. 2, 1972 in two steps. In the first step toluene is reacted with (21) Appl. No.: 294,129 chlorine in the presence of light, at a temperature in the range of 70 to 190°C and in at least two vessels or reactors. In the second step benzal chloride and resid 30 Foreign Application Priority Data ual benzyl chloride produced in the first step are con June 6, 1972 Germany...... 2227337 verted to benzotrichloride by reaction with an excess Oct. 22, 1971 Germany...... 252608 of chlorine at a temperature of from 70 to 190°C. The chlorine in the second step is diluted with an inert (52 U.S.C...... 204/163 R gas and like the first step the second step is carried out (5ll Int. Cl...... B01j 1/10 in at least two vessels and the residence time for the (58) Field of Search 204/163 R; 260/651 R, 651 HA reaction for the first and second steps in the ratio of 1.3 to 1.5. The ratio of chlorine to inert gas is regu 56) References Cited lated from vessel to vessel in the second step of the re UNITED STATES PATENTS action. l,828,858 10, 1931 Conklin...... 2041163 R 7 Claims, 1 Drawing Figure

PATENTED JUN11 1974

3,816,287 - 2 PHOTOLYTIC PROCESS FOR THE CONTINUOUS benzal chloride still present in the reaction mixture PRODUCTION OF BENZOTRICHLORIDE WITH A slows down considerably. The consequence of this is LOW BENZAL CHLORIDE CONTENT that although the resulting benzotrichloride contains smaller quantities of products which are chlorinated in the nucleus, the proportion of benzal chloride is too BACKGROUND high. This invention relates to a particularly advantageous process for the continuous production of benzotrichlo SUMMARY ride with a low benzal chloride content by which com It has now surprisingly been found that benzotrichlo prises chlorinating toluene. The formation of benzotri 10 ride having only a low benzal chloride content can eas chloride by the chlorination of toluene proceeds step ily be obtained in excellent yields by a simple continu wise via benzyl chloride and benzal chloride. On a large ous process comprising the chlorination of toluene at technical scale the production of benzotrichloride from elevated temperatures in the presence of light. In this toluene is carried out batchwise, leaving aside the pro process, toluene is first reacted with from 75 to 96 per cess described in DDR Pat. No. 5 100. However, 15 cent of the stoichiometric quantity of chlorine required when the continuous process of production is em for the formation of benzotrichloride. This reaction is ployed, the formation of by-products is difficult to pre carried out under the influence of light attemperatures vent. In the process according to DDR Pat. No. 15 100, of from 70 to 190°C in a first section comprising at the starting materials, toluene and chlorine, are reacted least two vessels. The benzal chloride and residual together by introducing them into benzotrichloride 20 quantities of benzyl chloride present in the reaction which has been heated to a temperature of at least 200 mixture are then converted into benzotrichloride by re to 205C, and benzotrichloride is continuously re acting them with an excess of chlorine diluted with moved from the reaction chamber at the rate of its for inert gas, the amount of chlorine used being up to 30 mation. Benzotrichloride obtained by this process, percent in excess of the total stoichiometric quantity however, contains about 0.4 percent of benzal chloride 25 required for the reaction of toluene. This reaction is and is, therefore, unsuitable for many purposes. Fur also carried out at a temperature in the range of from thermore, by repeating this known process it has been 70 to 190°C in a second section which also comprises found that benzotrichloride produced on a large tech at least two vessels. In this second section, the propor nical scale by this process varies in its quality owing to tion by volume of chlorine to inert gas is reduced from the variation in its benzyl chloride content and its con between 10 : 1 to 2 : 1 employed in the first vessel to tent of by-products which are chlorinated on the nu between 1 : 3 to 1 : 10 used in the subsequent vessel or cleus. This is demonstrated by the fact that when chlo vessels, and the residence times of the reaction mixture rine is introduced into pure, distilled benzotrichloride in the first and second sections are related to each under the conditions of the DDR Patent, substantial other in ratios of from 1 : 3 to 1 : 5. quantities of higher boiling and in part no longer distill 35 able products which are chlorinated at the nucleus are DESCRIPTION immediately formed, the formation of these products The reaction temperature is preferably 80° to 160°C proceeding particularly rapidly at the prescribed tem in the first chlorination section and 110° to 170°C in perature range for the reaction from 200 to 205°C. the second section. The quantity of chlorine used in the The quantity of by-products which are chlorinated in 40 first chlorination section is preferable 85 to 96 percent the nucleus is 16.5 percent after 3 hours continuous in of the stoichiometrically required quantity. The excess troduction of chlorine and rises to 22.4 percent after 5 chlorine diluted with inert gas used in the second sec hours. tion is preferably 10 to 25 percent. The ratio of chlo This quantity of by-products which are chlorinated in rine to inert gas in the second section ranges from the nucleus is formed even if the chlorine is not intro 45 about 5 : 1 to 2: 1, down to 1 : 5. The ratio of the resi duced into pure benzotrichloride but into a mixture dence time in section 1 to the residence time in section which contains a substantial quantity of benzyl chloride 2 is preferably about 1 : 4. The number of vessels in the and which is equal in its composition to the mixture first chlorination section is from two to seven, prefera which is inevitably formed before the benzotrichloride bly five or six. The number of vessels in the second stage is reached: - 50 chlorination section is from two to five, preferably Toluene: 0.1% three or four. According to a particularly advantageous Benzyl chloride: 9 % embodiment of the process of the invention, the vol Benzal chloride: 55 % Benzotrichloride: 34% ume of the vessels used in the last chlorination stage of By-products chlorinated in the 55 the second section is two to three times the volume of nucleus: 2% all the preceding vessels of sections 1 and 2. According to the process of the invention, the chlo When chlorine is introduced into this mixture under rine excess required to reduce the benzal chloride con the conditions indicated in DDR Pat. No. 15 100, the tent in the end product as much as possible is restricted proportion of by-products which are chlorinated in the to as few stages of the reaction as possible. In order to nucleus is 13.5 percent after only 2 hours and 17.6 per 60 suppress unwanted effects of the chlorine excess (in cent after 3 hours. creased formation of by-products which are chlori It is found that although the rate of increase in the nated in the nucleus), the invention also provides that formation of products which are chlorinated in the nu the required chlorine excess is diluted with gases which cleus slows down in the terminal phase of the prepara are inert in the reaction (for example nitrogen or hy tion of benzotrichloride due to the reduction in the 65 drogen chloride), preferably nitrogen. The process of amount of excess chlorine (based on the stoichiometri the invention may be carried out, for example in a nine cally required quantity), the rate of reaction with the stage chlorination apparatus (-with nine vessels) ar 3,816,287 3 4. ranged in cascade formation in two sections as already proved compared with the prior art (see following ex mentioned above, chlorine being introduced into the ample with arrangement of apparatus). first section (stages 1 to 5) in amounts of 2.3 to 2.9 The benzotrichloride obtained has many possible ap mol, preferably 2.6 to 2.9 mol, per mol of toluene, plications, for example as an intermediate product for which corresponds to about 86 to 96 percent of the the production of benzoyl chloride or for the produc stoichiometric quantity of chlorine required for the tion of coalitar dyes (see Ullmann's Enzyklopaedie der production of benzotrichloride from toluene, while in technischen Chemie, 3rd Edition (1954), Volume 5, the second section (Stages 6 to 9), the resulting reac page 460 and A. R8mpp, Chemielexikon 6th Edition tion mixture is chlorinated up to practically complete (1966), pages 645 and 646). formation of benzotrichloride with an excess of chlo O Example rine which must be diluted with inert gas. If the process of the invention is carried out using five Benzotrichloride is produced continuously in a plant vessels in the first section, the waste gases from the consisting of nine enamel vessels arranged in cascade third to fifth vessel which contain increasing propor formation behind one another, the first eight of which tions of unreacted chlorine as the degree of chlorina 5 have a capacity of 400 litres each and the ninth a ca tion of the reaction mixture increases, may be returned pacity of about 6 m (see FIG. 1). The procedure is as to the first and/or second vessel so that the waste gases follows: of the first section of chlorination have a chlorine con Each of the nine reaction vessels is equipped with a tent of less than one volume percent. Since the amount high pressure mercury immersion lamp (2,000 Watt). of chlorine used in the first section of the process ac Toluene is introduced into the first vessel at a uniform cording to the invention is less than the amount of chlo rate of 210 l/h and flows by gravity into the second, rine required for the chlorination of toluene to benzo third and subsequent vessel down to the ninth and is trichloride, the waste gases from vessels 3, 4 and 5 of chlorinated at the same time. the first section of the process may always be returned The addition of chlorine is subdivided into two sec 25 tions: The first section covers vessels 1 to 5, into which to the first two vessels of the first section without any chlorine is introduced at the rate of 129 m per hour. risk of chlorination of toluene in the nucleus or of the Based on the quantity of toluene used, this corresponds formation of any other by-products. This procedure to 2.9 times the molar quantity of 96.0 percent of the therefore contains a considerable technical advance. theoretical quantity required for formation of benzotri In the second section of the chlorination process, 30 which may consist, for example, of vessels 6 to 9, it is chloride. This rate of feed of chlorine, which is kept necessary to use an excess of chlorine, based on the constant, is subdivided as follows among vessels 1 to 5 quantity of chlorine required for the chlorination of tol vessel 1: 28 m/h of chlorine; vessel 2: 19 m/h of uene to benzotrichloride, in order to ensure complete chlorine; vessel 3: 38 m/h of chlorine; vessel 4: 29 chlorination of the reaction mixture from the first sec 35 m/h of chlorine; vessel 5: 15 m/h of chlorine. tion of the process into benzotrichloride. Provided the Already at the fifth vessel the chlorine introduced is procedures mentioned above are observed, this excess diluted with nitrogen (ratio by volume of Cl: N = 3 can safely be used without entailing any disadvantages : 1. or resulting in the formation of unwanted by-products. Since the waste gas contains an increasing proportion 40 of unreacted chlorine as the degree of chlorination in The number of chlorination vessels employed in the creases, the waste gases from vessels 3 to 5 are re process of the invention and the subdivision of the ves turned, that from vessel 3 being returned to vessel 2 sels into two sections may, of course, be varied even and that from vessels 4 and 5 to vessel 1. The chlorine more widely. The chlorine-containing waste gases from introduced is in this way made to undergo almost quan the second section of the process of the invention are 45 titative reaction, and the combined waste gas from ves advantageously conveyed directly to a separate pro sels 1 and 2 contains less than 1 percent of chlorine. duction plant where they may be used, for example, for The average residence time of the product flowing the production of benzyl chloride. Benzotrichloride ob through the apparatus is about 6.6 hours in the first tained as the product of the process according to the chlorination section (see Table 1). invention contains at the most 0.2 percent by weight of 50 The heat of reaction produced in the chlorination re benzal chloride and the proportion of products which action is removed from the reaction vessels by a contin are chlorinated in the nucleus is not more than about uous stream of cooling water (jacket cooling) adjusted 5.2 percent by weight. Benzotrichloride obtained by to the rate of flow of product. the process according to the invention therefore has a The reaction mixture from the first section of chlori purity of more than 94 percent by weight. The process, 55 nation still contains 2.0 percent of benzyl chloride and therefore, provides for a rational continuous produc 38.6 percent of benzal chloride in addition to 57.1 per tion of benzotrichloride of consistent quality at a high cent of benzotrichloride (see Table 2). production rate. It must be regarded as distinctly sur This mixture is continuously chlorinated in the sec prising that it is possible with a continuous method of ond section of chlorination (vessels 6, 7, 8 and 9) until operation to lower the benzal chloride content to below the benzal chloride content is only s 0.2. 0.2 percent and at the same time prevent the propor This requires 37 m of chlorine per hour, which cor tion of unwanted by-products, which are mainly prod responds to an excess of 23.2 percent. ucts chlorinated in the nucleus, from rising above 5.2 This quantity of chlorine is subdivided among vessels percent by weight, Thus, not only is the benzotrichlo 6 to 9 as indicated below and in addition diluted with ride product consistent in quality regardless of the out 65 increasing proportions of nitrogen: put rate of the plant but, furthermore, the yield based Vessel 6: 16 m of chlorine and 8 m of nitrogen per on the quantity of chlorine put into the process is im hour; 3,816,287 5 6 Vessel 7: 10 m of chlorine and 8 m of nitrogen per 15: HCl waste gas (Cly content () to 50 percent) hour, : Hg immersion lamp Vessel 8: 6 m of chlorine and 15 m of nitrogen per (x): Inflow valves to keep rate of supply constant hour, What is claimed is: Vessel 9: 5 m of chlorine and 25 m of nitrogen per 5 1. Process for the continuous production of benzotri hour. chloride which comprises: Cooling with water may be dispensed with in vessels a. in a first step, reacting toluene with from 75 per 6 to 8. Vessel 9 is maintained at a constant temperature cent to 96 percent of the stoichiometric quantity of (about 150°C) by heating with steam at a pressure of chlorine required for the formation of benzotri five excess atmospheres (temperature variation see O chloride, in the presence of light, at a temperature Table 1). in the range of from 70 to 190°C and in at least The waste gas from vessels 6 to 9 contains a high pro two vessels; and portion of unreacted chlorine (about 10 to 50 percent). b. in a second step, converting the benzal chloride The waste gases are utilized in adjacent production and residual quantities of benzyl chloride produced plants for the production of other products of chlorina 15 from the first step to benzotrichloride by reaction tion. at a temperature of from 70 to 190°C with an ex The average residence time in the second section of cess of chlorine of up to 30 percent based on the chlorination is 23.9 hours, of which 21.2 hours are total quantity of chlorine stoichiometrically re spent in the ninth alone (the last) (see Table 1). quired for the reaction with toluene, the chlorine The end product discharged from the ninth vessel being diluted with an inert gas, carrying out the contains 0.2 percent of benzal chloride and 94.4 per second step in at least two vessels in which the ratio cent of benzotrichloride. Its content in by-products of chlorine to inert gas is reduced from within the which are chlorinated in the nucleus and constituents range of from 10:1 to 2:1 in the first vessel to within which cannot be distilled is 5.2 percent. Further details the range of from 1:3 to 1:10 in subsequent vessels; may be found in Tables 1 and 2 below. 25 the residence times of the reaction mixture in the TABLE 1.- TABULATED suMMARY RELATING TO THE EXAMPLE Rate of throughput: (a) Raw material: 210 li?h of toluene (N185 kg/h.) 166 m.8/h. chlorine (~526 kg/h.); cor responding to r23% excess. (b) End product: 283 li?h. of benzotrichloride (~392 kg/h). Reaction conditions: Introduction of chlorine Addi- Based on the tion stoichiometric of quantity Ratio tol- required in- Nitrogen by vol- Time of Reaction lene, - - - inflow, ume of stay in tempera Reaction vessel l/h. m.3/h. Mol Percent m./h. Cla:N, hours ture, C. 28 0, 6 1.6 89 9 0.5 ... 4 96 38 0.8 .3 126 29 0, 6 1.2 130 15 0.4 1.1 156 129 2.9 6.6 ------16 0, 4 1.0 73 0 0.2 0.9 40 6 0.1 0.8 19 5 0. 21.2 151 Total Second section------37 0.8 .27.2 56 ------23.9 ------St. of first plus second sec- 210 66 3.7 23.2 61 ------30.5 ------Ol. w TABLE 2.--TABULATED suMMARY RELATING TO THE first and second steps being in the ratio of from 1:3 EXAMPLE to 1:5 Composition of the reaction product: 50 2. Process of claim 1 wherein the second step is car Percent by weight ried out in the presence of light. See ali: 3. Process of claim 1 wherein the reaction tempera Den- ESSEc ture is in- the range of from 80° to 160°C in the first step Reaction sity."... Tolu Benzyl Benzal Benzotri. "Nisingnucleus plus and from 110 0 a.to 170°Ccy in the second step. vessel 20° C. ene chloride chloride chloride residue 55 4. A process of claim 1 wherein the ratio of the resi

-- 1,1,018 110 28.456.4 35.149. 19.85.9 0.40.9 1,1.5 5 dence time in the1. first step to the residence time in the 1.227 i. 4 36.3 49.5 1.0 6 second step is 1:4. I. : : SS St. 3. 5. Process of claim 1 wherein the first step uses five 1.373------1.36i II. 0.010.2 17.27.2 - 89.379.6 3.32.9 60 to six vessels and the second stepp uses three to four vese l. 379 ------0.01 1. 3. : sels. 1. 386 ------0.0 0. 94. - 6. A process of claim 1 wherein each stage of both The reference numerals in the drawing showing the steps of the reaction is carried out in a separate reac arrangement of apparatus (FIG. 1) have the following tion vessel. meanings: 65 7. Process of claim 6 wherein the volume of the ves 1 to 9: Reaction vessels sel of the last stage of the second step is from 2 to 3 0: Toluene inlet times the volume of all the preceding vessels in the first 11, 12: Chlorine inlets and second steps. 13: Benzotrichloride discharge a. 14: HCl waste gas (Cl content --- 1 percent)